Problem- thermal expansion of lathe spindle bearings creating probem in threading

[jasminder]

friends,
i realized that when i turn my machine on the rpms are very accurate. say 900 in the dro and 900 in the demanded tab. But after a couple of minutes it comes down to 870 to 880.
Why?
thermal expansion?
then it starts making problems in thread cutting. The pitch changes and the probelm begins. How to handle this problem? any experiences?
I think it is because of thermal expansion that jams the spindle a little bit.

regards,
jasminder singh

[jasminder]

is something left to configure in mach?

[ad64075]

What make/model machine?

[jasminder]

Originally Posted by ad64075 What make/model machine?

hi friend,

it is a homemade cnc here
YouTube - C:\Documents and Settings\Administrator\Desktop\100_6190_flv.flvbuild log is also on cncnzone.
i am using mach3 here
regards,
jasminder singh

[ad64075]

I'm going to guess that your longitudinal feed is not in sync with your spindle. Meaning that as your spindle slows, the feed does not, causing the pitch to decrease (less threads per unit). This will happen if your program feeds in inches per minute instead of using feed per revolution. Does your machine have feedback/encoder on the spindle?

[jasminder]

Originally Posted by ad64075 I'm going to guess that your longitudinal feed is not in sync with your spindle. Meaning that as your spindle slows, the feed does not, causing the pitch to decrease (less threads per unit). This will happen if your program feeds in inches per minute instead of using feed per revolution. Does your machine have feedback/encoder on the spindle?

yes friend,
it has an encoder and i am using g95 mode in my entire program (feed per rev). But i am not using g95 in the threading cycle somewhere (how can i use it) it looks like
g76 x...z...p 0.035.. and some thing something. I will confirm it soon.
But is it possible to put feed per rev in threading cycle too? then how

[ad64075]

With most machines, you would issue the feed per rev command in the same line as the cycle you wish to execute. Using your example: G95 G76 X... Z... and so on.